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Vincenzo Coscia - One of the best experts on this subject based on the ideXlab platform.

  • FIRST-ORDER MACROSCOPIC MODELLING OF HUMAN CROWD DYNAMICS
    Mathematical Models and Methods in Applied Sciences, 2008
    Co-Authors: Vincenzo Coscia, C. Canavesio
    Abstract:

    This paper deals with the mathematical modelling of crowd dynamics within the framework of continuum mechanics. The method uses the Mass Conservation Equation closed by phenomenological models linking the local velocity to density and density gradients. The closures take into account movement in more than one space dimension, presence of obstacles, pedestrian strategies, and modelling of panic conditions. Numerical simulations of the initial-boundary value problems visualize the ability of the models to predict several interesting phenomena related to the complex system under consideration.

  • first order models and closure of the Mass Conservation Equation in the mathematical theory of vehicular traffic flow
    Comptes Rendus Mecanique, 2005
    Co-Authors: Nicola Bellomo, Vincenzo Coscia
    Abstract:

    This article deals with a review and critical analysis of first order hydrodynamic models of vehicular traffic flow obtained by the closure of the Mass Conservation Equation. The closure is obtained by phenomenological models suitable to relate the local mean velocity to local density profiles. Various models are described and critically analyzed in the deterministic and stochastic case. The analysis is developed in view of applications of the models to traffic flow simulations for networks of roads. Some research perspectives are derived from the above analysis and proposed in the last part of the paper. To cite this article: N. Bellomo, V. Coscia, C. R. Mecanique 333 (2005).

  • on a closure of Mass Conservation Equation and stability analysis in the mathematical theory of vehicular traffic flow
    Comptes Rendus Mecanique, 2004
    Co-Authors: Vincenzo Coscia
    Abstract:

    Abstract This Note deals with the development of mathematical methods for the closure of the Mass Conservation Equation for macroscopic hydrodynamical models of traffic flow on roads. The closure is obtained by a phenomenological model, relating the local mean velocity to local density earlier in time. An evolution Equation is obtained for the flux and a stability analysis is performed; this qualitatively describes some features of congested flow. To cite this article: V. Coscia, C. R. Mecanique 332 (2004).

Laurent Jacquin - One of the best experts on this subject based on the ideXlab platform.

  • Taylor's hypothesis convection velocities from Mass Conservation Equation
    Physics of Fluids, 2011
    Co-Authors: Samuel Davoust, Laurent Jacquin
    Abstract:

    We propose to use the continuity Equation to calculate convection velocities provided by the Taylor hypothesis for flow structures crossing a measurement plane. This is carried out in Fourier space to identify a velocity associated to each frequency. High-speed PIV experimental data of an axisymmetric mixing layer is used to implement the method. We show that as expected the Taylor hypothesis fails for the lowest frequencies and predicts the convection velocity to be close to the mean velocity for the higher ones. The method is compared to one of the definitions proposed by Del Alamo and Jimenez [J. Fluid Mech. 640, 5 (2009)].

Tomohide Nishiyama - One of the best experts on this subject based on the ideXlab platform.

  • Accuracy and limitations of vector flow mapping: left ventricular phantom validation using stereo particle image velocimetory
    Journal of Echocardiography, 2017
    Co-Authors: Rei Asami, Tomohiko Tanaka, Kenichi Kawabata, Kunio Hashiba, Takashi Okada, Tomohide Nishiyama
    Abstract:

    Background The accuracy of vector flow mapping (VFM) was investigated in comparison to stereo particle image velocimetry (stereo-PIV) measurements using a left ventricular phantom. VFM is an echocardiographic approach to visualizing two-dimensional flow dynamics by estimating the azimuthal component of flow from the Mass-Conservation Equation. VFM provides means of visualizing cardiac flow, but there has not been a study that compared the flow estimated by VFM to the flow data acquired by other methods. Methods A reproducible three-dimensional cardiac blood flow was created in an optically and acoustically transparent left-ventricle phantom, that allowed color-flow mapping (CFM) data and stereo-PIV to be simultaneously acquired on the same plane. A VFM algorithm was applied to the CFM data, and the resulting VFM estimation and stereo-PIV data were compared to evaluate the accuracy of VFM. Results The velocity fields acquired by VFM and stereo-PIV were in excellent agreement in terms of the principle flow features and time-course transitions of the main vortex characteristics, i.e., the overall correlation of VFM and PIV vectors was R  = 0.87 ( p  

  • Accuracy and limitations of vector flow mapping: left ventricular phantom validation using stereo particle image velocimetory.
    Journal of echocardiography, 2016
    Co-Authors: Rei Asami, Tomohiko Tanaka, Kenichi Kawabata, Kunio Hashiba, Takashi Okada, Tomohide Nishiyama
    Abstract:

    Background The accuracy of vector flow mapping (VFM) was investigated in comparison to stereo particle image velocimetry (stereo-PIV) measurements using a left ventricular phantom. VFM is an echocardiographic approach to visualizing two-dimensional flow dynamics by estimating the azimuthal component of flow from the Mass-Conservation Equation. VFM provides means of visualizing cardiac flow, but there has not been a study that compared the flow estimated by VFM to the flow data acquired by other methods.

Caterina Calgaro - One of the best experts on this subject based on the ideXlab platform.

  • A combined Finite Volumes -Finite Elements method for a low-Mach model
    International Journal for Numerical Methods in Fluids, 2019
    Co-Authors: Caterina Calgaro, Claire Colin, Emmanuel Creusé
    Abstract:

    In this paper, we develop a combined Finite Volumes - Finite Elements method based on a time splitting to simulate some low-Mach flows. The Mass Conservation Equation is solved by a Vertex-Based Finite Volume scheme using a $\tau$-limiter. The momentum Equation associated with the compressibility constraint is solved by a Finite Element projection scheme. The originality of the approach is twofold. First, the state Equation linking the temperature, the density and the thermodynamic pressure is imposed implicitly. Second, the proposed combined scheme preserves the constant states, in the same way as a similar one previously developed for the variable density Navier-Stokes system. Some numerical tests are performed to exhibit the efficiency of the scheme. On the one hand, academic tests illustrate the ability of the scheme in term of convergence rates in time and space. On the other hand, our results are compared to some of the literature by simulating a transient injection flow as well as a natural convection flow in a cavity.

  • A combined finite volume - finite element scheme for a low-Mach system involving a Joule term
    AIMS Mathematics, 2019
    Co-Authors: Caterina Calgaro, Claire Colin, Emmanuel Creusé
    Abstract:

    In this paper, we propose a combined finite volume-finite element scheme, for the resolution of a specific low-Mach model expressed in the velocity, pressure and temperature variables. The dynamic viscosity of the fluid is given by an explicit function of the temperature, leading to the presence of a so-called Joule term in the Mass Conservation Equation. First, we prove a discrete maximum principle for the temperature. Second, the numerical fluxes defined for the finite volume computation of the temperature are efficiently derived from the discrete finite element velocity field obtained by the resolution of the momentum Equation. Several numerical tests are presented to illustrate our theoretical results and to underline the efficiency of the scheme in term of convergence rates.

  • An Hybrid Finite Volume-Finite Element Method for Variable Density Incompressible Flows
    Journal of Computational Physics, 2008
    Co-Authors: Caterina Calgaro, Emmanuel Creusé, Thierry Goudon
    Abstract:

    This paper is devoted to the numerical simulation of variable density incompressible flows, modeled by the Navier-Stokes system. We introduce an hybrid scheme which combines a Finite Volume approach for treating the Mass Conservation Equation and a Finite Element method to deal with the momentum Equation and the divergence free constraint. The breakthrough relies on the definition of a suitable footbridge between the two methods, through the design of compatibility condition. In turn, the method is very flexible and allows to deal with unstructured meshes. Several numerical tests are performed to show the scheme capabilities. In particular, the viscous Rayleigh-Taylor instability evolution is carefully investigated

Michael L. Van Woert - One of the best experts on this subject based on the ideXlab platform.

  • Atmospheric Wind Retrievals from Satellite Soundings over the Middle- and High-Latitude Oceans
    Monthly Weather Review, 2002
    Co-Authors: Cheng-zhi Zou, Michael L. Van Woert
    Abstract:

    Abstract A technique that uses satellite-based surface wind and temperature soundings for deriving three-dimensional atmospheric wind fields is developed for climate studies over the middle- and high-latitude oceans. In this technique, the thermal wind derived from the satellite soundings is added to the surface wind to obtain a first-guess, nonMass-conserved atmospheric wind profile. Then a Lagrange multiplier in a variational formalism is used to force the first-guess wind to conserve Mass. Two Mass Conservation schemes are proposed. One is to use the meridional Mass transport Conservation Equation as a constraint to derive the meridional wind first, and then the vertically integrated Mass Conservation Equation is used to infer the zonal wind. The zonal and meridional winds are obtained separately in this approach. The second scheme is to use the vertically integrated Mass Conservation Equation as a constraint to retrieve the zonal and meridional winds simultaneously from the first-guess field. Temperat...